GF, Grammatical Framework, is a programming language for multilingual grammars, used in the MOLTO project to build translation systems. How to write GF grammars is specified in the numerous tutorials and manuals available via http://grammaticalframework.org. This report explains the compiler of the GF language: how GF source code is compiled to various formats usable in runtime systems, how the developers can test their grammars, how other formats (such as lexica and example sentences) can be converted to GF code, how to call the compiler in various ways.